This invention relates to a method and apparatus for loading a holder for loading an article to be treated as a semiconductor substrate, for example a silicon wafer or a glass mask or a reticle, on a stage in an evacuated treating chamber or casing in which a circuit pattern is depicted on the wafer, the glass mask or the reticle with an electron beam or the dimension of the wafer, glass mask or a reticle is measured with an electron beam.
In a modern integrated circuit of extremely high density, for example, several tens of thousands or one million or more bits on one chip, the line width depicted is extremely narrow of the order of submicrons. Accordingly, it is a practice to depict a circuit pattern on a relatively large glass mask and then transfer printing the circuit pattern onto the surface of the wafer by reducing the size of the depicted circuit pattern. To simplify the description, in the following, a case wherein the circuit pattern is depicted directly on the surface of a semiconductor wafer will be described.
Taking apparatus for depicting a circuit pattern with an electron beam as an example, one example of a prior art loading apparatus will firstly be described with reference to FIG. 6. The apparatus shown therein comprises an electron beam circuit pattern depicting apparatus 11, a loading apparatus 12, and an electron beam column 14 mounted on a casing 13 constituting an evacuated treating chamber. Although many types of the electron beam irradiating device are known, one disclosed in the specification of Japanese Patent Publication No. 54906/1982 is considered suitable. A saddle 16 is mounted on a base 15 at the bottom of casing 13 to be movable toward left and right, and a stage 17 is mounted on saddle 16 to be movable in a direction perpendicular to the sheet of drawing. A holder 18B securely holding a semiconductor (for example silicon) wafer, not shown, is mounted on the stage 17. The direction of movement in the X and Y directions of rectangular coordinates and the position of holder 18B are controlled by moving saddle 16 and stage 17 with a suitable driving mechanism, not shown. The casing 13 is constituted by an upper plate 13A, side walls 13B and a bottom plate 13C which are formed with passages, not shown, for passing water at a constant temperature for maintaining various elements contained in the casing at a predetermined constant temperature. By ON.cndot.OFF controlling and deflecting electron beam 14a as in a raster scanning system or a vector scanning system, a circuit pattern can be depicted on the wafer mounted on the stage.
The loading apparatus 12 comprises a sealable casing 21 connected to casing 13 through a valve 22. A magazine 23 housed in casing 21 is connected to an elevating mechanism 24 via rod 25. In the magazine 23 are contained holders 18A, 18C and 18D in the order mentioned. Either one of these holders is loaded and unloaded onto and from stage 17 by a loader 26 at the same level as holder 18B in the casing 13. A second space from upper of magazine 23 is shown vacant since holder 18B which had occupied this space has been loaded in casing 13. When depiction of the circuit pattern on the substrate held by holder 18B is completed, it is transferred into magazine 23. Then the magazine 23 is elevated by one pitch by elevator mechanism 24, and the holder 18C is loaded.
In the loading apparatus of the type described above, to remove a holder carrying a wafer whose pattern writing has been completed and to load a new holder on the magazine 23, valve 22 is closed and then inert gas such as N.sub.2 is admitted into casing 21 through a leak valve, not shown. A door, not shown, of the casing 21 is opened to exchange the already treated holder with a new holder. Then a vacuum pump, not shown, is operated to evacuate a space 21A in the casing 21. At this time magazine 23 and the newly loaded holder would be cooled due to adiabatic expansion of gas which has been filled in space 21A. For this reason, even when the temperature of a holder is made equal to that of stage 17 before loading the holder into magazine 23, the temperature of the holder becomes much lower than that of the stage 17. Accordingly, when such a cold holder is loaded on the stage 17, not only the temperature of the holder would vary on the stage thus making it difficult to ensure accurate positioning but also the temperature of the stage would be varied. Moreover, as magazine 23 is moved it is difficult to maintain it at a desired constant temperature by passing water at the constant temperature directly through the magazine. When a square holder made of aluminum having a side length of l=170 mm is subjected to a temperature variation of 0.5.degree. C., the amount .DELTA.l of its thermal deformation is expressed by the following equation: EQU .DELTA.l=l.times..alpha..times.1=170.times.23.5.times.10.sup.-6 .times.0.5=0.002
where .alpha. represents the linear expansion coefficient of aluminum Thus, .DELTA.l is equal to about 2 microns. Suppose now that the temperature of the holder has varied by 0.5.degree. C. by the heat transmitted from the stage 17 while the holder loaded on stage 17 is being depicted with a circuit pattern. Then the dimension of one side of the holder varies by about two microns which presents a fatal problem.